squeal

Hey thanks! I had some idea about this, but wasn't quite sure how best to do it. That solution looks pretty solid.

D'oh! Should have searched better first: http://www.midibox.org/forum/index.php?topic=4386.msg28609#msg28609 Although I have 2.5-5V, not 0-2.5V. I don't think I can change it either. hmmmm....

So, due to the peculiarities of the guitar synth resistive fretboard shenanigans, I am looking at a design where the output voltage from the fretboard would be between 2.5 and 5 volts. Is there a way to fix this in the code? I would want 2.5V to send a 0 CC value, and 5V to send a 127(max) CC value. Linear scaling in between. I did look at the example at the bottom of this page: http://www.ucapps.de/mios_c.html but it seemed that that would only change the max and min midi values. I want to change the max and min AIN input values. Does this make sense?

Thanks TK :) Hrmmm.... One better is twice as resolved.....

Hey guys, one more question: Does anyone know what the resolution of the midiboxFM's pitch bend parameter is? I searched the documentation on ucapps, but couldn't find this info. I was thinking of using a Yamaha tx81z as a kind of "target" synth in designing my guitar controller, but it uses only 7 bit pitch bend (as opposed to 14 bit). I will be using pitch bend with very wide ranges in my guitar controller, so I need any synth I connect to to have the highest possible resolution. Thanks. :)

Update in case anyone is interested..... I found this paper on DIY carbon doped resistive ink: http://nime.org/2006/proc/nime2006_230.pdf and so I have been trying to sort out that approach for the resistive fretboard.

Yeah, I guess I shouldn't beat my head against the wall with this one. I have enough on my plate. After all, the kit is like $25 at smashTV. Cool. I think you've brought me to my senses.

So I am mulling the idea of incorporating the midiboxFM synth into my guitar-like midi controller. Is this even possible using a single core module? I need to use an AIN module to run the controller, which will have pots and CV ins. I can do without the swanky control surface and 2X40 LCD of the FM, and just edit the sounds from the pc, but I would like to be able to navigate through saved patches away from the pc. It seems to me like it's doable, but I will have to either alter the midiboxFM code to incorporate the AIN, or somehow add the midiboxFM stuff to midibox64. Am I totally crazy? Is this too much for the core to handle?

I'm afraid I still don't understand what's wrong with the vhs tape (or other resistive strip) method. Each string is isolated, and a separate strip of resistive material is glued to the neck directly under each string. The strip is part of a voltage divider which sends a voltage depending on where you finger it. ;) The only issue I can see is that vhs tape has a resistance around 1Mohm per foot, and the resistance between my fingers is also around 1Mohm, so the neighboring strings could mess up eachother's pitches. Now if I could find a material with a much lower resistance, say 10Kohm/foot, then the resistance between my fingers would be negligible. Or I could play with rubber gloves on....... But seriously, is there something I'm missing here?

You can't insulate the strings from each other when you play a barre chord.

Ya but in this case I wouldn't be really sliding anything against the resistive element, just pressing down the stationary string at different points, assuming I can resist the urge to "bend" notes side to side as on a normal fretted guitar. ;)

I bet you're right about the wearing down of the resistive element. Maybe there are more robust resistive materials than vcr tape? Antistatic packaging is supposed to have resistive qualities. But that's also just plastic. I'm sure the companies that make slider pots would know about robust resistive strips. ;) Here's a question: What value pots are suggested for use with the ain module? What values are allowable?

I haven't really seen the diode matrix design, but it seems that barre chords would frustrate any design using solid metal frets. ???

Cheater: In the opening post I mentioned the graph tech ghost bridge saddle pickups. They are bridge saddles with piezo elements mounted inside. These were designed with hex output in mind, so I imagine that they would get good individual output with minimal crosstalk.

I don't think it has. The Hagstrom was monophonic, The stepp thing had some kind of plastic frets or something. I don't think there has ever been a polyphonic guitar synth with standard metal frets and metal strings. I could be wrong, though.

I don't think you could use normal frets and achieve polyphony.

On second thought maybe I will do the envelope followers all in hardware. Then I could have some CV outs to plug into my MG-1 and rock out analog style. ;D

I will look into that. I guess it depends how much time it will take and how successful I feel I could be.

OK so we talked about this project a bit in the "simple DSP inside Core Module?" thread, but I wanted to give an overview here. The plan is to build a guitar-like midi controller for use with midi synthesizers. The strings of the guitar will be essentially ribbon controllers with vhs tape glued to a fretless guitar neck. From these circuits I will extract a pitch value and either quantize it and apply it at note-on or turn it into a cc to be applied to the synth's pitch bend parameter. Other, more exotic uses could probably be tested with ease once I have built it. The strings will run over graphtech ghost bridge saddles which also act as individual pickups. (If anyone knows of a less expensive polyphonic pickup system, let me know. They are $100) Each string's amplitude will be converted by some means into midi-cc values, with the intent to apply these to a synth's volume parameter. I have some experience in analog electronics and some c programming, but am new to pics and designing midi controllers, so I appreciate any input you guys have.

OK so I've been mucking about with some VST code putting bit reduced audio into envelope followers, and I'm fairly convinced that any signal degradation due to the bit reduction causes negligible change to the envelope. I mean this depends on the env folloewer's parameters and structure, but I think that in most cases it won't matter. Specifically, I compared 44.1k audio into env follower with 4.41k audio into env follower, and the outputs looked about the same. New question: The C code envelope follower I am thinking of using is comprised of 2 cascaded single pole filters. There is more to it than that, but that is the part I want to implement in code. So, for four channels I would need to do 8 individual single pole filters. Could the pic reasonably handle this using the mios framework?

Now I do want it to twiddle the volume parameter of my synth engine, among other possible uses. I don't really need it to be very guitar like in the shape of the transient, but I do want it to be as fast as possible. A slow attack would make it less satisfying to play, I would imagine.

OK cool. I'm going for it. :D No real reason to not try it. Also, the "audio" that I will be tracking is kind of irrelevant, so I can tailor it to the processing. I am tracking the vibrations of guitar strings, and I am not using the audio for any other thing. The strings could all be tuned to the same note for all I care. I just want it to feel like a normal guitar and extract a usable envelope. Tomorrow is payday, so I'll order the pcbs and such and get started. Thanks everyone for the info and advice. :)

THAT looks pretty easy. Maybe I will use.......THAT.

I definitely will :) @ nebula: do I REALLY have to build envelope followers? :-[ What is that sample rate?

OK based on what A.C. says I am gonna go ahead and give this a shot. If I can't do a digital env follower in the box, then I will just go ahead and build analog env followers. Does anyone know what the sample rate of the AIN module is? Same as the core(40mhz)? If anyone has any thoughts or questions on this project, let me know.